Blast furnaces are used in the manufacture of iron, such furnaces including multiple (e.g. 38) oil and hot gas (e.g. air) injection path(s). Oil and hot gas are injected into a blast furnace through tuyeres that are attached to corresponding blowpipes, which is known in the art. A furnace may have, for example, thirty-eight or so different gas/oil injection ports. The converted energy produced (e.g. about 140.0 BTUs of heat/gallon of oil) reduces the need for the more expensive coke/BTU product.
Blockage of an injection port may occur, for example, as a result of material falling and accumulating in front of the tuyere nozzle. If left undetected or unclogged, oil may back up in the blowpipe, possibly causing a flood or other undesirable furnace condition(s). Thus, we have the need for detecting such clogging or blockage.
Prior art systems for detecting clogged or blocked tuyeres are known in the art. One prior art system includes a circuit where a set point is selected to determine whether a relay picks up or drops out. This turns indicators on or off to display strong or weak signals. This circuit/system has problems in processing weak signals effectively, as there are no calibration or adjustment procedures, and no references to follow. Furthermore, it is difficult for this system to isolate problems, and maintain signal strength. Optical fiber bundles used for light detection are susceptible to breaking, being scratched by dirt accumulation, and degradation. Also, the signal has to overcome a minimum threshold level (1 vdc) before it becomes noticeable in this prior art system.
U.S. Pat. No. 5,481,247 discloses a blast furnace tuyere sensor system, including generating analog voltages from tuyere sensors in order to monitor light intensity trends of all tuyeres in the furnace. Alarms are actuated when light intensity becomes abnormally low or abnormally high. By continuously detecting and measuring changing intensity of light from each blast furnace tuyere, and actuating alarms when the measured analog voltage signal deviates from a base load voltage by more than a predetermined percentage, both bright tuyeres and blocked tuyeres are detected. For example, in the '247 patent, the base load may be fifty percent (50%) of the sensor voltage span, and alarms are actuated when the measured voltage is either from 5-10% (blocked tuyere) of the voltage span or from 85-90% (bright tuyere) of the voltage span. The '247 patent also requires a complex system for detecting if and when a sensor emits a straight line signal, or becomes unstable via erratic swings in measured voltage, and generates alarm signals in response thereto. Unfortunately, the system of the '247 patent is undesirable because: (i) it requires a potentiometer to adjust the circuit voltage to a mid-point base load value; (ii) it lacks as to efficient calibration; (iii) it requires complex circuitry or the like which detects and looks for straight line and unstable signals; (iv) it sets off alarms only when the measured voltage is below or above the base load by greater than a certain percentage; (v) undesirable amplification characteristics and calibration are used; (vi) the optical fiber connected to each sensor is susceptible to scratches, breakage, too small of a light gathering area, and adverse effects due to moisture; and (vii) circuit flaws or problems are not easily identifiable.
U.S. Pat. No. 5,397,108 discloses a peepsight for a blast furnace tuyere sensor system, but does not disclose or suggest circuitry or the like to overcome the problems with the '247 patent set forth above. The '108 patent also suffers from the problem that the illustrated optical fiber or cable is disadvantageous for the reasons discussed above.
It is apparent from the above that there exists a need in the art for an improved system and corresponding method for detecting potential clogging of blast furnace injection paths, the improved system including efficient calibration techniques, efficient means of identifying circuit problems or errors, efficient light intensity detection proximate the peepholes, efficient and simple circuitry, the ability to detect both strong and weak signals, and circuitry enabling easy isolation of problems using external calibration. This invention will now be described with respect to certain embodiments thereof, accompanied by certain illustrations wherein: